Brake slack adjuster mechanism



Nov. 10, 1964 H. B. HUNTRESS ETAL BRAKE SLACK ADJUSTER MECHANISM Original Filed Nov. 3, 1959 m if Q N: 9 9 LI. Ll.

5 Sheets-Sheet 1 ATTORNEYS HOWARD a. HUNTRESS I BY THOMAS s. TAYLOR 1964 H. B. HUNTRESS ETAL 3,156,096

BRAKE SLACK ADJUSTER MECHANISM 5 Sheets-Sheet 2 Original Filed Nov. 3, '1959 um mw M3 FR M. m R D W3 4 TNVI mUA VH W s wm K A w 0 M HT ww US N mdE ATTORNEYS Nov. 10, 1964 H. B. HUNTRESS ETAL BRAKE SLACK ADJUSTER MECHANISM Original Filed Nov. 3, 1959 5 Sheets-Sheet 3 INVENTORS. HOWARD B. HUNTRESS y THOMAS S. TAYLOR B ATTORNEYS Nov. 10, 1964 H. B. HUNTRESS ETAL 3,156,095

BRAKE SLACK ADJUSTER MECHANISM Original Filed Nov. 3, 1959 5 Sheets-Sheet 4 a dawn zl/ 6K ATT NEYS United States Patent Ofi ice 3,156,096 Patented Nov. 10, 1964 3,156,ll% ERAKE SLACK ADJUSTER MEiINISM Howard B. Huntress and Thomas S. Taylor, Sufi'ern, N .Y., assignors to American Brake Shoe Company, New York, NY a corporation of Delaware ()riginal application Nov. 3, 195 Ser. No. 850,697, now Patent No. 3,053,349. Divided and this application Jan. 23, 1962, Ser. No. 168,132

4 Claims. (6i. oil-54.5)

This invention relates to brake structure for railroad vehicles, and in particular to the Wheel cylinders that actuate the brake shoes of the railroad cars. This application is a division of application Serial No. 850,697, filed November 3, 1959, now Patent No. 3,053,349.

The majority of railroad vehicles now in use utilize a mechanical linkage for transmitting a braking force from an air cylinder of a pneumatic system to individual brake shoes which are suspended adjacent the wheels of the vehicle. This mechanical system is relatively heavy and incorporates an intricate linkage arrangement which introduces undesirable forces on the trucks and car body.

Under the present invention there is substituted a hydraulic system for the mechanical linkages now in use in railroad cars in a manner such that the hydraulic system utilizes the existing pneumatic system as a signal system and power source. Moreover, the braking action in a vehicle equipped with the present hydraulic system is compatible with railroad vehicles now in use but not provided with the present hydraulic brake system. This enables the vehicle so-equipped to be used in interchange and still perform its braking function when associated with cars equipped with a standard air-mechanical brake system.

After repeated applications of the vehicle brakes over extended periods of time the individual brake shoes are worn down by frictional contact with the wheels to such an extent as to necessitate adjustment so that the brake shoes all maintain proper clearance with their respective wheels, and so that in applying the brakes, air cylinder travel is not excessive.

It is an object of this invention to incorporate in a hydraulic system for actuating railroad vehicle brakes individual hydraulically actuated cylinders, each of which includes an automatic slack adjuster mechanism of novel construction for maintaining preselected spacing between the wheel-engaging surface of a brake shoe and the opposed surface of a corresponding wheel. It is a related object of the present invention to enable such a slack adjuster mechanism to pay out slack in the event that an emergency braking strain may cause a temporary overadjustment of such an extent that the brakes would remain applied after the braking signal ceases. The ability of a slack adjuster to pay out slack in such instances is highly desirable since such over-adjustment can result in locked brakes, dragged wheels and power losses. It is another object to utilize such an automatic slack adjuster to conserve the amount of air required by the actuating pneumatic system, to reduce the actual consumption of air and thereby permit the total capacity of the pneumatic system to be reduced. Such reduction in the over-all capacity of the pneumatic system enables smaller air reservoirs to be utilized, and these smaller reservoirs can be recharged in less time than present conventional railroad brake systems which utilize mechanical linkages as the brake actuating structure.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principle thereof and what is now considered to be the best mode contemplated for applying that principle. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art Without departing from the present invention and the purview of the appended claims.

FIG. 1 is a fragmentary plan view of a part of a railroad vehicle under the frame showing the manner in which a hydraulic system constructed in accordance with this invention is incorporated with a conventional pneumatic system;

FIG. 2 is a fragmentary side elevation of a railroad vehicle with a sectional view through the truck taken in the direction of the arrows 22 in FIG. 1;

FIG. 3 is an end elevation of a railroad vehicle with a sectional view through the truck taken in the direction of the arrows 3-3 in FIG. 1;

FIG. 4 is a side elevation view, in section, of one embodiment of a hydraulic master cylinder utilized in the arrangement illustrated in FIG. 1;

FIG. 5 is a side elevation view, in section, of a hydraulic wheel cylinder utilized in the arrangement shown in FIG. 1;

FIG. 6 is a somewhat schematic view showing, in section, the various component parts of the hydraulic system in their unactuated positions;

FIG. 7 is a somewhat schematic view showing, in section, the various component parts of the hydraulic system in the respective positions assumed subsequent to a pneumatically applied braking force;

FIG. 8 is a somewhat schematic View showing, in section, the various component parts of the hydraulic system in the respective positions assumed subsequent to application of a manually applied braking force;

FIG. 9 is a side elevation view, in section, of another embodiment of a wheel cylinder which can be utilized in the arrangement illustrated in FIG. 1; and

FIG. 10 is a side elevation view, in section, of another embodiment of a wheel cylinder which can be utilized in the arrangement illustrated in FIG. 1.

Referring now to FIGS. 13 of the drawings, a railroad vehicle, shown as a box car, is designated generally by the reference numeral 21. The car 21 includes an under frame UP and car trucks at either end of the car. One truck .22 is illustrated in FIGS. 1-3. The truck 22 comprises a bolster indicated by the reference character B, two side frames S1 1 and SP2, and two wheel axles WAll and WAZ. The axles are provided with wheels W in the usual manner and are rotatably mounted in journal boxes IE on the side frames in a conventional manner.

In accordance with this invention a plurality of individual hydraulic wheel cylinders 23, 24, 25, and 26 are mounted adjacent each of the Wheels W of the railway car 21. As illustrated in FIG. 1, the side frames include brake beam slots BBS which are formed on the inner sides of the side frames and are normally employed with unit brake beams in a conventional mechanical linkage. The wheel cylinders 23; to 26 are each formed with a projecting flange and are mounted on the brake beam slots BBS by bolts 27 which are passed through apertures in the flanges of the wheel cylinder. As best viewed in FIG. 2, brake heads BH are carried by the individual wheel cylinders and brake shoes BS are in turn mounted on the brake heads Bl-l. The brake heads for the wheel cylinders 23 and 26 are tied together by a pair of upper and lower tie rods 28 and 29 respectively, and the brake heads for the wheel cylinders 24 and 25 are likewise tied together by a pair of upper and lower tie rods 31 and 32. The brake heads Bl-I are mounted on the wheel cylinders a manner such that the brake heads are movable laterally with respect to the wheel cylinders by the connecting tie rods to take care of the lateral movement '3: which must be permitted to the wheel and axle. his mounting arrangement may preferably include a slotted construction at the end of the wheel cylinder pistons as Will be more fully described with reference to FIG. 5.

The railroad car 21 includes a pneumatic system designated generally by the reference numeral 33. The pneumatic system 33 includes a main air line 34 which connects each car in the train to a common source of air pressure and also includes auxiliary and emergency air reservoir tanks 35A and 35B. A brake-regulating valve 36 is connected to the main airline 3-; by a conduit 37 and is connected to the auxiliary and emergency reservoir tanks by conduits 38 and 3? respectively. The pneumatic system 33 also includes a main air cylinder 41 which is connected to the brake regulating VZIlX 36 by a conduit 42.

The main air cylinder 41 is connected to actuate a hydraulic system which includes a hydraulic master cylinder 43 and the individual wheel cyhnders 2 3 to 26 heretofore described as being mounted on the side frames SP1 and SP2. As viewed in H65 1 and 2, a shaft 44 of the main air cylinder is received within an end plate of a dust guard bellows 45 mounted at one end of the master cylinder 43. As will be described in greater detail hcreinbelow, the shaft 44 is operative to move an internal piston within the master cylinder to supply pressurized hydraulic fluid to each of the individual wheel cylinders to initiate a braking action. Conduit means are connected between the master cylinder and the wheel cylinders for the purpose of transmitting such pressurized fluid. These conduit means comprise a first conduit 46 which is directly connected to the master cylinder and joined in a T-connection to a conduit 47 which extends along the length of the car 21 between th car trucks. Branch conduits 3S and 45 interconnect the conduit 47 with the wheel cylinders adjacent each of the side frames.

An hydraulic reservoir and a manually actuated hydraulic pump, which affords a hand brake, are each connected to the master cylinder 43 through a common hydraulic conduit. As viewed in FIG. 3, a tank 51 is mounted in a fixed postion at one end of the boxcar 21. The tank 51 contains hydraulic fluid and thus aiiords a reservoir of hydraulic fluid for the master cylinder 4-3. A conduit 52 interconnects the tank 51 and the master cylinder 43. As described in greater detail in the aforesaid application, a pump is immersed within the fluid contained within the tank 51 and may be actuated by means of an hand lever 53 to pump a pressurized hydraulic fluid through the conduit 52 to the master cylinder and through the conduits 46 and 47 to move the individual brake shoes into frictional engagement with the respective wheels W of the railroad car. It will be noted that the tank 51 and the hand lever 52 are positioned so that the hand brake can be easily applied by a person standing on a ladder 54 at the end of the railroad car.

In the apparatus thus far described the elements in the pneumatic system and the car trucks represent conventional or standard structure and are present on the majority of the railroad vehicles now in use. However, in place of the mechanical linkage that would normally be connected to the main air cylinder 41 to engage the brake shoes into the wheels, a novel hydraulic system including the master cylinder 43, wheel cylinders 23 to 26, and the hydraulic hand brake has been substituted therefor.

In the operation of the braking system thus far described, a braking action is initiated by a braking sign-a being applied to the brake-regulating valve 36 in a known manner. Such a braking signal positions the valve to supply air from the reservoir 35A through the conduits 38 and 42 to the main air cylinder 4-1. The piston and shaft 44 of the main air cylinder ,is extended axially outwardly to force pressurized hydraulic fluid from the interior of the master cylinder 43 through the conduits 46 and 47 to the individual wheel cylinders. The

pistons of the individual wheel cylinders are in turn actuated outwardly of the respective cylinders to engage the brake shoes in frictional contact with the wheels and brake the car 21. Because the wheel cylinders are mounted directly on the brake beam slots the reaction forces are transmitted to the side frames rather than the car body and bolster as in the conventional mechanical linkage. The tie rods 23432 interconnect the two brake shoes which are applied to the wheels mounted on the same axle and shift the shoes laterally of the wheel cylinders with lateral movement of the axle. Alternatively, the brakes may be applied by a person pumping the hand lever 53 to transmit pressurized hydraulic fluid 'hrough the conduit 52 to the interior of the master cylinder 3 and thence to the individual wheel cylinders.

Each individual wheel cylinder incorporates an automatically operating slack adjuster which compensates for any wear of the brake shoes by moving the brake head and shoe nearer the wheel to maintain a predetermined spacing between the shoe and the wheel and thereby aliord eliective and uniform braking by all of the brake shoes throughout the useful life of the shoes.

Referring now to FIG. 4 of the drawings, there is illustrated a detailed sectional view of the master cylinder 41. The cylinder 41 comprises a pair of end plates 56 and 57 and a tubular housing 53 which extends therebetween and provides an inner bore 6t within the master cylinder. A main piston 59 is axially reciprocable within the bore 60 and includes a shank 61 of reduced diameter which has a tapered recess at 62 formed in an end thereof. The shaft 44 of the main air cylinder 41 is received within the recess 62 and is operative upon actuation of the main air cylinder to force the piston 59 inwardly of the master cylinder in the manner described hereinabove. The housing 58 is retained within an annular recess 63 in the end plate 56 and a recess 64 formed in the radially inner portion of an annular flange 65. The flange 65 is in turn supported from the inner face of the end plate 57. A plurality of tie rods 66 extend through apertures 67, 68, and 69 in the respective end plate 56, flange 65, and end plate 57 and nuts 71 are threaded on the ends of the tie rods to pull the end plates toward one another and retain the tubular housing 58 therebetween.

The external diameter of the piston 59 is somewhat smaller than the internal diameter of the tubular housing 58, and a long stroke diaphragm 72 is fastened to the head of the piston and the outer cylinder to provide a positive nonleaking sealing arrangement between the piston and the outer housing. The inner flange of the diaphragm 72 is clamped between the head of the piston 59 and a pressure plate 73 by a plurality of cap screws 74. The outer flange of the diaphragm '72 is clamped between an end plate 57 and the annular flange 65 by nuts 76. Thus, the diaphragm 72 divides the bore 60 into separate chambers and 75.

The end plate 57 has a first, centrally located aperture 77 extending axially therethrough and the conduit 52, which leads to the reservoir, is threaded in the aperture 77. The end plate 57 includes an additional aperture 73, and the conduit 46, which leads to the individual wheel cylinders, is threadedly connected in the aperture 78. Thus, the piston and the long stroke diaphragm define an enclosed volume 70 within the bore 60 of the master cylinder, and this enclosed volume communicates with the reservoir and the wheel cylinders through the conduits 52 and 46.

The end plate 56 is formed with a centrally located aperture 79 which extends axially therethrough and which mounts a sleeve-type bearing 81 therein. The sleeve bearing 31 in turn encircles and supports the shank 61 of the piston. The end plate 56 also includes a pulrality of holes 82 which extend axially through the end plate and which are disposed radially outwardly of the central aperture 7 9. These holes 82 communicate the interior of the dust guard bellows 45 with that portion of the inner bore 65 which is not filled with hydraulic fluid, and thus act to vent that portion of the inner bore to permit free reciprocation of the piston 59 within the bore. The dust guard bellows 45 acts as a shield to prevent the entry of dust or other foreign mater into the inner bore as a result of such venting action through the communicating holes 82.

The dust guard bellows 45 is clamped at opposite ends to the end plate 56 and the outermost end of the shank 61 to provide a fluid-tight seal around the shank 51. The connection to the end plate 56 is afforded by a slight recess 83 in one face of the end plate and a pressure plate 34. The pressure plate 84 is interposed between the nut 71 and the end plate 56 so as to firmly clamp the outer flange of the bellows 45 which is received within the recess 33. The connection to the shank 61 is afforded by a pair of relatively thin plates 86 and 37 which receive the inner flange of the bellows 45 therebetween and which are clamped together by a plurality of cap screws 88 threaded in the outer end of the shank 51.

The piston is formed with an annular flange 89 at the base end thereof and this flange 89 serves as a support for a portion of the long-stroke diaphragm when the piston is at maximum stroke. A high rate spring stack 81) may preferably be interposed between the piston 59 and the inner face of the end plate 55 to provide compensation for temperature variations, and consequent volume variations in the hydraulic fluid during operation of the hand brake in a manner presently to be described. A return spring 91 is seated at opposite ends on the inner face of the end plate 57 and the base surface of an annular recess 90 which is formed in the head of the piston 59. The spring 91 affords a biasing force for returning the piston 59 to the position illustrated in FIG. 4 at the completion of a brake actuating stroke of the master cylinder.

Valve means, indicated generally by the reference numeral 92, are disposed within the chamber 70 adjacent the end of the conduit 52 which is connected to the hydraulic reservoir. The valve means 92 are normally open, as illustrated in FIG. 4, to communicate the chamber 71) with the hydraulic reservoir, but are movable to a closed position to interrupt the communication between the master cylinder and the reservoir during a pressuretransmitting stroke of the piston 59.

The valve means 92 include an annular housing 93 which has a flanged portion seated within a recess 94 in the inner face of the end plate 57. The annular housing 93 includes a plurality of slots 95 which form ports for communicating the chamber 711 with the conduit 52. The annular housing 93 also includes a radially inwardly projecting lip or flange 97 at the axially innermost end of the housing. A piston 98 is axially slidable within the housing 93 between the positions limited by the lip 97 and the inner faces of the end plate 57. The piston 98 has an annular groove formed in the face which engages the end plate 57, ad an O-ring 99 is mounted in the groove and is compressed to provide a fluid-tight seal when the piston 98 abuts the end plate 57. In this position of the piston the communication of the bore 611 with the reservoir through the conduit 52 is interrupted. Thus, the piston 98 acts as a valve element to regulate fluid flow through the slots 96. The surface of the piston 98 which faces the end plate 57 is also provided with a circular recess 101 and a return spring 102 is seated at opposite ends in the recess 101 and the inner face of the end plate 57. The spring 1132. affords a biasing force for returning the piston 98 to the normally open position as illustrated in FIG. 4.

Another coil spring 103 is seated at one end on the surface of the piston 98 which faces the main piston 59. The other end of the coil spring 1113 is seated within a circular recess 1114 formed in the head of the main piston 59. The spring 1113 is so adjusted that it is just unloaded when the main piston 59 abuts the end plate 56 in the fully retracted position of the main piston 59 within the master cylinder.

While the description of the operation of the master cylinder 41 will be described more fully hereinafter with relation to the other components of the hydraulic system, it should be noted at this time that only a slight amount of movement of the main piston 59 inwardly of the master cylinder is required for the force developed by the spring 1113 to become sufficient to overcome the force afforded by the spring 1112 and move the piston 98 rightwardly, as viewed in FIG. 4, to a position wherein the O- ring 99 is compressed and seals off the interior of the master cylinder from the hydraulic reservoir.

Referring now to FIG. 5 there is illustrated in sectional side elevation an individual wheel cylinder constructed in accordance with this invention. In FIG. 5 the wheel cylinder is indicated generally by the reference numeral 20 and comprises a base plate 106 and a housing 1117 having an inner bore 108 therein. The base plate 106 is attached to one end of the housing 167 by a plurality of cap screws 1119. At the end opposite that mounting the base plate 1% the housing 107 is formed with a radially inwardly projecting flange 111 and a sleeve bearing 112 is mounted in the inner periphery of the flange 111.

A main actuating piston 113 is slidably mounted at one end within the sleeve bearing 112 for axial movement in and out of the bore 113%.

As in the construction of the master cylinder 41, the wheel cylinder includes a long stroke diaphragm which affords a fluid-tight seal between the main piston and the outer housing. Thus, in the wheel cylinder 20 an outer flange of a long stroke diaphragm 114 is clamped be tween the housing 167 and the base plate 1%. The inner flange of the long stroke diaphragm 114 is clamped between the head of the piston 113 and a plate 115 which is mounted on the piston by a plurality of fillet head screws 117. Preferably the plate 116 includes a slight flange 116E which clasps the diaphragm 114 about a rounded edge of the head of the piston 113. The long stroke diaphragm divides the interior of the cylinder 20 into separate chambers 118 and 119 on either side of the diaphragm.

The base plate 1% includes a sleeve member 121 which projects from an inner face of the base plate and which extends axially inwardly of the cylinder parallel to the sides of the bore 108.

The inner surface of the sleeve member defines a bore and the outer surface of the sleeve member includes a plurality of radially extending lugs 122 which engage the side walls of a circular recess 123 which is formed in the head end of the piston 113. The innermost end of the sleeve member 121 abuts an annular base surface 125 of the recess 123 to limit the extent of the movement of the piston 113 axially inwardly of the housing 107. The piston 113 also includes a recess 124 formed in the base surface 125.

A return spring 126 is seated at opposite ends on the inner face of the flange 111 and the base of an annular recess 127 which is formed in the surface of the piston facing the flange 111 and biases the piston inwardly. of the housing 107.

The sleeve member 121 is formed with a plurality of apertures 123 which extend radially therethrough and interconnect the chamber 119 with the inner bore 120.

The base plate 1% is formed with a central inlet opening 129, which may preferably have internal pipe threads as illustrated and which affords a connection to a conduit leading to the master cylinder 43.

A slack adjuster piston 131 is slidably mounted within the bore 120 and has one end 131E formed with a reduced diameter so as to clear the retaining ring 134'. The surface of the piston 131 which faces the inner surface of the base plate 166 is formed with an annular groove 132 and O-ring 133 is mounted therein so as to be compressed by movement of the piston 131 to the extreme leftward position illustrated in FIG. 5. Such compression of the O-ring 133 affords a fluid-tight seal which prevents any flow of hydraulic fluid past the O-ring and to the port 129. The extent of the movement of the slack adjuster piston 131 toward the main actuating piston 113, rightwardly as viewed in PEG. 5, is limited by a snap ring 134' which is seated in an annular groove 135 formed in the bore 120.

The slack adjuster piston 131 includes an inner bore 134 in the surface facing the inlet port 129 and also includes an orifice 136 which extends axially through the head of the piston and communicates the bore 13 within the slack adjuster piston with the chamber 119. The base surface at the bottom of the bore 134 is formed with a generally concave recessed surface 137 in the area surrounding the orifice 136 and a valve 138, which is slidably mounted within the bore 134, has a generally hemispherical-shaped projection which is shaped complementary to the concave recess 137 and is engageable therein to block any fluid flow through the orifice 13-5. The valve includes ports 13% which extend through the body of the valve to permit fluid flow therethrcugh. A snap ring 141 is seated in an annular groove formed in the cylindrical surface of the bore 134 and affords a support for a spring retainer 142. A return spring 143 is seated at opposite ends on the spring retainer 142 and a recessed surface 144 of the valve. Thus, the valve 138 is biased to a normally closed position wherein the valve blocks any flow through the orifice 135.

In a normally closed position of the valve, as illustrated in FIG. 5, the slack adjuster piston 131 defines an expansible chamber 140 Within the portion of the bore 120 that is confined between the slack adjuster piston and the base plate 106. The slack adjuster piston and the main actuating piston 113 define another expansible chamber therebetiveen which is the chamber 112 as described hereinabove. This latter chamber is sealed from the expansible chamber 140 by the Oring which is compressed into engagement with the inner face of the plate 106 in the disposition of the parts illustrated in FIG. 5. The force causing such compression of the O-ring 133 is generated by the return spring 126 and is transmitted through the incompressible hydraulic fluid contained in the chamber 119.

As illustrated in FIG. 2, each of the wheel cylinders is inclined at a slight angle from the horizontal. Thus, any air in the hydraulic fluid within the wheel cylinders rises to the convolution at the upper portion of the diaphragm 114. For the purpose of bleeding such air from the hydraulic system, the base plate 106 has a bleed tube 146 mounted on an inner face thereof so as to extend in close proximity to the convolution in the long stroke diaphragm. A bleeder hole 147 is formed in the base plate 106 and communicates the interior of the bleed tube 146 with a head seal on one of the cap screws 1%.

The outer end of the piston 113 is formed with a T- shaped slot 143 which is adapted to receive a complementary T-shaped lug of one of the break heads therein. The mounting arrangement afforded by the T-shaped slot permits the brake head to slide horizontally through the T-shaped slot so that the brake head and brake shoe can move laterally of the wheel cylinder to compensate for lateral movement of the wheels and axles with respect to the side frames on which the wheel cylinders are mounted.

While the description of the operation of the wheel cylinder will be described in relation to the operation of the other component parts of the hydraulic system of this invention hereinafter and with reference to FIGS. 6, 7 and 8 of the drawings, the manner in which the slack adjuster piston functions to take up slack and the manner in which the foot valve 13% functions to pay out slack will now be briefly described.

Assuming that a hydraulic pressure is applied to the expansible chamber Lit) through the inlet port 129 with the disposition of the component parts of the Wheel cylinder 20 as illustrated in FIG. 5, the volume of the chamber 146 is increased by movement of the slack adjuster piston 131 rightwardly within the bore 120, as viewed in FIG. 5. Simultaneously, the force developed within the chamber 1 10 is transmitted through the incompressible hydraulic fluid contained in the chamber 119 defined between the main piston and the slack adjuster piston, and the main piston 113 is forced axially outwardly of the housing 197 to move the brake shoe toward the periphery of the car wheel.

The adjuster piston 131 normally moves a distance which is equal to the distance D between its beveled edge 1318 and the ports 123. This motion of the adjuster piston normally causes sufiicient motion of the output piston 113 to cause the brake shoe to be engaged in frictional contact with the periphery of the wheel and apply a braking force to the wheel. However, as the brake shoes wear down the gap between the brake shoe and the wheel increases so that the main piston 113 must be moved outwardly of the housing some additional amount. In such a case the hydraulic pressure in the chamber 140 roves the slack adjuster piston 131 to a position wherein the beveled edge 13 1B uncovers the ports 123 to communicate the expansible chamber 11) directly with the master cylinder through the chamber 1 th and the inlet port 139. The hydraulic fluid thus permitted to fiow into the chamber 119 increases the volume of this chamber and exerts a force on the piston 113 to move the piston axially outwardly and engage the brake shoe with the car wheel.

Upon cessation of the braking effort and consequent decrease in the hydraulic fluid pressure within the chamber 14d, the return spring 126 moves the main piston 113 axially inwardly of the housing 107, and the force of the spring 126 is transmitted through the hydraulic fluid in the chamber 119 to move the slack adjuster piston 131. This return movement of the piston continues until the slack adjuster piston is returned to the position illustrated in FIG. 5 and in which the O-ring is compressed to form a fluid-tight seal between the two chambers 14% and 119. However, the main piston 113 cannot return to the position illustrated in FIG. 5 because the volume of the chamber 119 was increased by the amount of the fluid which was admitted through the ports 123 on the brakeapplying stroke of the wheel cylinder. Therefore, the main piston 113 does not return to the limit position wherein the annular base face 125 abuts the end of the sleeve member 121 but is stopped at a different position wherein the original clearance between the brake shoe and the wheel, which existed prior to any wearing down of the brake shoe, has been restored. The seal afforded by the compressible O-ring 133 prevents any leakage of fluid from the chamber 119 to the inlet port 129 which would tend to increase this clearance. Thus, the cylinder 29 automatically adjusts the starting position of the brake shoe to compensate for any wearing down of the brake shoe so that on a subsequent actuation of the brakes, the brake shoe will be engaged with the wheel without requiring the slack adjuster and piston to move a greater distance than the distance D.

If some unusual situation should arise which would cause such over adjustment of the slack adjuster as to necessitate the paying out of some slack by decreasing the volume of the expansible chamber 119, or in the event that it is necessary to decrease the volume of this chamber during replacement of a worn out brake shoe, the construction of the valve 138 afiords means for paying out slack by decreasing the volume of the chamber 119. In such a case it is necessary only that a force of a predetermined magnitude be applied to the outer end of the main piston 113. Such a force is transmitted through the hydraulic fluid contained within the chamher 119 and acts on the valve 138 to overcome the bias of the return sprign and unseat the valve. Hydraulic fluid then flows through the orifice 136 and the orifices 13h and out the inlet port 129 to the master cylinder and alternately to the reservoir. Such a decrease of the volume of the chamber 119 permits the piston 113 to be retracted inwardly of the housing 167 to the position illustrated in FIG. wherein the annular base surface 125 abuts the end of the sleeve member 121.

The overall operation will now be described in connection with FIGS. 6, 7 and 8. In these figures, the master cylinder, reservoir, and hand pump, and an individual wheel cylinder are somewhat schematically illustrated. The structural parts however correspond to the parts de scribed in detail with reference to FIGS. 4 and 5 and like reference numerals are used to designate like parts but with the addition of the suflix A in FIG. 6, B in FIG. 7, and C in FIG. 8.

In FIG. 6 the disposition of the parts illustrated is that assumed with the system at rest but with the automatic slack adjuster mechanism of the wheel cylinder 29A operative to compensate for a slight amount of brake shoe wear as noted by the legend. Thus, it will be noted that the surface 125A of the piston 113A is slightly spaced from the end of the sleeve member 121A, rather than being engaged with the end of the sleeve member as illustrated in FIG. 5, and this spacing results from a slight amount of hydraulic fluid having been trapped within the chamber 119A on some previous braking cycle or cycles.

In FIG. 6 the valve 153A in the hydraulic reservoir is open so that the reservoir communicates through the conduit 52A and the ports 96A with the chamber 70A of the master cylinder to replenish any quantity of fluid which may have been required by operation of the slack adjusters in the individual Wheel cylinders.

In FIG. 7 the disposition of the parts of the hydraulic system is that assumed subsequent to a braking action resulting from an actuation of the main air cylinder of the pneumatic system. In such pneumatic actuation of the system, the air cylinder shaft 44B moves the piston 59B of the master cylinder inwardly of the cylinder and displaces hydraulic fluid from the chamber 'itlB to the individual wheel cylinders. The pressure generated by such movement of the piston 59B is transmitted through the hydraulic fluid within the chamber 70B and acts in conjunction with the force of the spring 193B to move the piston 933 against the bias of the return spring 1923 to the position wherein the sides of the piston cover the ports 96B and the seal 99B is compressed to a fluid-tight, sealing relation with the inner face of the end plate 573 to thereby seal off the conduit 52B and prevent any loss of pressure from the chamber 703. In this instance the positions of the parts of the hand pump are the same as that illustrated in FIG. 6.

In FIG. 7 the parts of the wheel cylinder B are illustrated as being positioned to supply hydraulic fluid from the master cylinder to the chamber 115 13 to compensate for some wearing down of the brake shoe. Thus, the slack adjuster piston 131B is shown engaged with the stop 134B. In this position of the slack adjuster piston the ports 128B are uncovered and hydraulic fluid is admitted to the chamber 119B to move the main piston 113B outwardly of the cylinder and independently of any axial movement of the slock adjuster piston. Upon cessation of the braking effort, as applied by the shaft 44B, the return spring 126B is effective to move the pistons 113B and 1313 leftwardly as viewed in FIG. 7 to close the ports 12813 and trap the extra fluid admitted to the chamber 1198 in the manner more fully described with relation to FIG. 5 hereinabove.

111 FIG. 8 the disposition of the parts of the hydraulic system is that produced by actuation of the hand brake. In this instance the valve 158C is closed so that downward movement of the piston 168C to the position illustrated in FIG. 8 is effective to overcome the bias of the spring 2020 and move the check valve 201C to an open position wherein the pressurized fluid within the chamber 1810 is displaced from the chamber and through the conduit 52C to the master cylinder. This flow of pressurized fluid passes through the ports 5960 of the normally open valve 920 and thereafter flows from the chamber 70C through the conduit 46C to the wheel cylinder 20C to actuate this wheel cylinder in the same manner as if the braking action were initiated by the main pneumatic cylinder.

In FIG. 8 the parts of the wheel cylinder 20C are again illustrated as being positioned to compensate for slack caused by wearing down of the brake shoe.

In FIG. 9 there is illustrated another embodiment of a wheel cylinder constructed in accordance with this invention. The wheel cylinder illustrated in FIG. 9 incorporates a lip-type seal reather than a long stroke diaphragm type of seal as illustrated in FIG. 5. Insofar as the parts of the wheel cylinder illustrated in FIG. 9 correspond to like parts of the wheel cylinder illustrated in FIG. 5, like reference numerals are used by with the addition of the In FIG. 9 a wheel cylinder is indicated generally by the reference numeral 201) and includes an outer housing 1WD which is suitably joined to a base plate 106D. A piston 113]) is slidable within an inner bore 108D of the housing and is supported by a bearing 112D mounted within an inwardly projecting flange at the end of the housing opposite that connected to the base plate. A T-shaped lug 211 is formed on the outermost end of the piston 113D and is adapted to mount a brake head and brake shoe assembly thereon in a manner such that the brake head is laterally movable with respect to the cylinder ZtBD.

A coil spring 1261) is seated at opposite ends on an inner face of the flange 111D and a base surface of an annular recess 127D in the piston 113]). The return spring 126D biases the piston inwardly of the housing 107D to a position where the bottom of the inner cavity of the piston 113D contacts the outer annular face of the sleeve member 121D, thus limiting the inward movement of the piston. The outermost cylindrical surface of the piston 113]) is formed with a groove 214 and a resilient liptype seal member 215 is disposed therein. The seal member 215 is of a U-shape in section and is aligned in the groove 214 so as to have one flange in engagement with the periphery of the bore 108D and another flange in engagement with the base surface of the groove 214. Thus, fluid under pressure transmitted to the central portion of the seal member 215 acts to flex the flange members in opposite radial directions to positively engage the outer flange with the periphery of the bore and the inner flange with the cylindrical surface of the base of the groove and thereby afford a fluid-tight seal between the piston and the bore 1081).

The cylinder 20]) also includes an axially extending sleeve member 121D which projects from the inner face of the base plate H561). The outer periphery of the sleeve member 121D incorporates a grooved construction which is received within an axially extending bore 123D of the piston 113D and which affords additional support for the piston within the housing. The sleeve member 1211) includes an inner bore D and a plurality of apertures 128D extend radially through the sleeve member to communicate the interior of the sleeve member with the exterior thereof. As in the embodiment of the wheel cylinder illustrated in FIG. 5, the Wheel cylinder 20D includes a slack adjuster piston 131D which is axially slidable within the bore 120D and which defines an expansible chamber 1191) within the main piston and another expansible chamber D within the sleeve member 121D on the side of the slack adjuster piston opposite that facing the main piston. An inlet port 129D is centrally located in the base plate 196D for communicating the cham- 11 ber 1401) with the master cylinder. A valve 138D is spring biased to a position wherein the valve closes off an axially extending aperture 136D formed in the head of the slack adjuster piston.

The operation of the wheel cylinder 20D is like that described in detail with reference to the cylinder illustrated in FIG. and will therefore only be briefly described at this time. Upon a fluid pressure being transmitted to the chamber 140D the slack adjuster piston and the main piston are both moved by reason of the hydraulic fluid contained in the chamber 119D therebetween. Normally the brake shoe carried by the piston 113D is engaged with the periphery of the car wheel prior to such movement of the slack adjuster piston 131D as would uncover ports 128D and communicate chamber 119D and the head end of the main piston directly with the inlet 129D. However, if there has been sufiicient wear at the face of the brake shoe on a previous braking cycle, such movement of the main and slack adjuster piston may be necessitated as to result in the slack adjuster piston moving to a position wherein such fluid flow through the ports 128D occurs. The pressurized fluid thus transmitted to the chamber 119D compensates for the wearing down of the brake shoe by moving the main piston axially outwardly while the slack adjuster piston is retained against the fixed stop 134D.

Throughout all phases of the operation of the power cylinder 29D hydraulic fluid pressure is effective to flex the seal 215 to prevent the escape of fluid to the chamber 113D.

The valve 138D permits slack to be paid out by exerting a force of a sufficient magnitude on the outermost end of the piston 113D in the same manner as described in detail with reference to FIG. 5.

Another embodiment of a wheel cylinder is illustrated in FIG. and designated generally by the reference numeral 301. In this instance the cylinder 301 includes an outer housing defined by an end cap 302 which mates with a cylinder piece 303 at respective radially projecting flange portions 304 and 306. The flanges 304 and 366 are formed with a plurality of circumferentially spaced openings 307 and 30S, and Allen head cap screws 369 are passed therethrough and have nuts 311 threaded on the ends of the cap screws to clamp the end cap to the cylinder piece. The end cap 302 and cylinder piece 333 are formed with an internal bore 312 of constant internal diameter which extends for substantially the entire length of the cylinder 301.

The cylinder piece 303 includes an inwardly projecting flange 313 at the end opposite that mating with the end cap 302, and the flange 313 terminates in an axially extending sleeve 314 which forms a support for a main piston 316 which is reciprocal within the bore 312. As illustrated in FIG. 10, the sleeve 314 includes a relatively short radially projecting flange 317 on the inner circumference thereof. A bushing 318 is disposed on the inner side of the flange 317 and retained in position by a retaining ring 319, while a scraper-type seal guide 321 is disposed in the annular recess defined on the opposite side of the flange 317.

The piston 316 includes a rod portion 322 which is slidable within the bushing 318 and engaged by the scraper-type seal 321. The outermost end of the rod portion 322 is formed with a T-shaped lug 323 for mounting a brake head and brake shoe thereon.

The end cap 392 includes a passageway 324 which is adapated to be connected to the master cylinder to supply hydraulic fluid from the side of the cylinder 301 to the interior thereof.

A slack adjuster piston 326 is formed with an axially projecting flange 327 at the outer periphery thereof and this flange adapts the piston 326 for reciprocation within the portion of the bore 312 defined by the end cap 302. The extent of reciprocal movement of the piston 326 is limited in one direction by abutment of the piston with an inner surface 328 of the end cap 302 and in the oppo- 12 site direction by engagement of the flange 327 with a ring 32? mounted within an annular groove formed in the side walls of the bore 312.

Thus, it will be seen that the main and slack adjuster pistons 316 and 326 define a first expansible chamber 331 therebetween and within the bore 312. The piston 326 also defines a second expansible chamber 332 within the portion of the bore 312 formed in the end cap 302.

In accordance with this invention the piston 316 is of a slightly smaller diameter than the diameter of the bore 312 and includes an axially extending sleeve 333 which affords a skirt on which a portion of a long stroke diaphragm 334 rests. The long stroke diaphragm 334 is clamped between the mating portions of the end cap 302 and 303 and extends across the bore 312 as illustrated in FIG. 10. Thus, the diaphragm 334 is continuous and requires no connection to the piston 316. It will be apparent from FIG. 10 that the diaphragm 334 forms a fluid-tight seal at one end of the chamber 331.

As a safety measure, an additional scaling device is preferably formed between the piston 31.6 and the bore 312 to maintain effective operation of the wheel cylinder 301 in the event that the diaphragm 334 should be ruptured. The structure affording such a safety seal includes a radially projecting flange 336 formed at the extremity of the skirt 333. An annular groove 337 is formed in the flange 336 and a resilient member, preferably an O-ring 333 fitted with a Teflon cap, is disposed within the groove 337 so as to be engaged in fluid-tight sealing relation with both the side walls of the bore 312 and the groove 337.

Provision is made for bleeding the chamber 331 to remove any air which may become entrapped therein. The structure for accomplishing such bleeding action includes an unloaded sealing screw 339 threaded within an opening 341 formed in a side wall of the end cap 302. In this instance the bleed screw is closely adjacent the convolution in the diaphragm 334 so that no auxiliary bleed tube is required.

The side walls of the end cap 302 are also formed with a plurality of circumferentially spaced slots 342 which form passageways for transmitting hydraulic fluid from the chamber 332 tothe chamber 331 subsequent to a predetermined extent of movement of the piston 326 as will be presently described. In the position of the piston 326 as illustrated in FIG. 10 flow of fluid through the passageways 342 is etfectively blocked by the flange 27. Additional sealing means in the form of an O-ring 343 disposed within an annular recess 344 formed in the piston 326 are provided for insuring that there be no seepage of fluid from the chamber 331 to the chamber 332 in the illustrated position of the piston 326.

The two pistons are biased to the positions illustrated by a pair of coil springs 346 and 347, each of which is seated at opposite ends of the piston 316 and the flange 313. In this instance the coil springs 346 and 347 are oppositely wound so as to minimize twisting of the diaphragm 334 from spring rotation caused by compression of the springs during an output stroke of the wheel cylinder.

A filtered drain and vent opening 348 is formed in the cylinder piece 303 on the air side of the piston 316 for venting this portion of the bore 312 during reciprocation of the piston 316.

The wheel cylinder 301 is effective to compensate for slack caused by a wearing down of the brake shoes in the following manner. Application of high pressure hydraulic fluid to the interior of the chamber 332 through the passageway 324, which is connected to the master cylinder, forces the piston 326 away from the end cap, rightwardly as illustrated in FIG. 10. Such movement of the piston 326 transmits a force through the hydraulic fluid trapped between the main and adjuster pistons and causes movement of the piston 316. Normally the brake shoe carried by the brake head mounted on the lug 323 is engaged with the car wheel prior to such movement of the piston 326 as would communicate the chamber 332 with the slots 342, and thus the chamber 331. Thus, upon cessation of the braking effort as applied by the master cylinder the return springs 346 and 347 are effective to return the pistons to the positions illustrated in FIG. with no change in the volume of the chamber 331. However, if there has been sufiicient wear at the face of the brake shoe on a previous braking cycle, such movement of the main piston 316 and slack adjuster piston 326 may be necessitated as to result in the slack adjuster piston moving to a position wherein this piston uncovers the slots 342 so as to communicate the chamber 332 with the chamber 331. Thus, the slack adjuster piston 326 may move from a first position wherein the passageways 342 are blocked to a second position, against the retaining ring 329, wherein the passageways communicate with the chamber 332. In this second position the pressurized hydraulic fluid increases the volume of the chamber 331 to force the main piston outwardly of the bore until the brake shoes are engaged with the car wheel. As in the other embodiments of the wheel cylinders, the return springs exert a biasing force through the hydraulic fluid contained within the chamber defined between the two pistons to move the adjuster piston back to a position wherein the piston blocks flow through the passageways 342 to thereby trap the increased volume of hydraulic fluid between the two pistons.

In some cases it may be necessary to decrease the axial spacing between the two pistons, and valve means 351 are provided in the adjuster piston 326 to enable this to be accomplished. The piston 326 may preferably be formed with an arched configuration in the central portion there of, as illustrated, so that a bored rivet 352 may be disposed within an opening 353 extending through the piston 326 in a manner such as to obviate any possibility of interference of the projecting portions of the rivet with other component parts of the wheel cylinder 351. In this instance the rivet 352 is formed with an internal L- shaped bore 354 and a small helical spring 356 is seated at opposite ends on the piston 326 and a retaining ring 357 mounted at one end of the rivet. The spring 356 normally biases the rivet 352 to the position illustrated in FIG. 10 wherein an O-ring 358 in the head of the rivet is compressed to sealing relation about the periphery of the aperture 353 to prevent any how of fiuid through the bore 354 of the rivet. However, a force of a predetermined magnitude may be exerted on the main piston 316 in the direction indicated by the arrow X to pressurize the fluid the chamber 331 and unseat the rivet 352 to thereby decrease the volume of the chamber 331 by transferring fluid through the bore 354 to the chamber 332.

It will be seen from the foregoing that under the present invention, an automatically operating slack adjuster is incorporated in each individual wheel cylinder to take up any slack caused by wearing down of the brake shoes. Additionally, each individual wheel cylinder incorporates mechanism for paying out slack in the event that some emergency strain causes an over-adjustment of the slack adjuster.

Hence, while we have illustrated and described the preferred embodiments of our invention, it is to be understood that these are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim: I

1. Hydraulic slack adjuster mechanism comprising, an outer cylinder including an outer housing having an axially extending inner bore and a base member extending across one end of the housing, a first piston reciprocal within the bore, a sleeve member projecting from an inner face of the base member and spaced radially inwardly from the outer cylinder and having an aperture extending radially therethrough, a second piston reciprocal within the sleeve member, said first and second pistons defining a first expansible chamber therebetween, said second piston defining a second expansible chamber within the sleeve member, said second piston being slidable between a first position wherein the second piston blocks fluid flow between the first and second chambers through the aperture to trap fluid within the first expansible chamher and a second position wherein the piston permits communication between the first chamber and the second chamber through said aperture to adjust the first piston, biasing means including a return spring acting for biasing the first piston inwardly of the bore and exerting a force through hydraulic fluid in the first chamber to move the second piston from the second to the first position, and a static seal eifective between the second chamber and the second piston in its first position to prevent leakage of trapped fluid from the second chamber in the adjusted position of the second piston whereby a force applied to the second piston by pressurized fluid supplied to the second expansible chamber is transmitted to the first piston through the trapped fluid in the first expansible chamber and is effective to move the second piston a predetermined distance between said first and second positions prior to any fluid being supplied to the first expansible chamber through said aperture.

2. Mechanism as defined in claim 1 wherein the first piston has an annular groove formed therein and a resilient member is disposed in the groove and forms a seal between the piston and the surface of the bore.

3. Hydraulic slack adjuster mechanism comprising, an outer cylinder including an outer housing having an axially extending inner bore, a first piston reciprocable within the bore, a sleeve member inward of the outer cylinder and aifording an inner cylinder, said sleeve having an aperture extending radially therethrough, a second piston reciprocable within the sleeve member, said first and second piston defining a first expansible chamber therebetween, means in association with said second piston defining a second expansible chamber therewith, said second piston being slidable between a first position wherein the piston blocks fluid fiow between the first and second chambers through the aperture to trap fluid within the first expansible chamber and a second position wherein the piston permits communication between the first chamber and the second chamber through said aperture to adjust the first piston, biasing means including a return spring acting on the first piston for biasing the first piston inwardly of the bore and exerting-a force through hydraulic fluid in the first chamber to move the second piston from the second to the first position, and a static seal effective between the second chamber and the second piston in its first position to prevent leakage of trapped fluid from the second chamber in the adjusted position of the second piston whereby a force applied to the second piston by fluid supplied under pressure to the second expansible chamber is transmitted to the first piston through the trapped fluid in the first expansible chamber and is effective to move the second piston a predetermined distance between the first and second positions prior to any fluid under pressure being supplied to the first expansible chamber through said aperture.

4. Mechanism as defined in claim 3 wherein the second piston includes normally closed valve means adapted to be opened by pressure of a predetermined magnitude in the first chamber tending to move the second piston to its first position.

References Cited in the file of this patent UNITED STATES PATENTS 

1. HYDRAULIC SLACK ADJUSTER MECHANISM COMPRISING, AN OUTER CYLINDER INCLUDING AN OUTER HOUSING HAVING AN AXIALLY EXTENDING INNER BORE AND A BASE MEMBER EXTENDING ACROSS ONE END OF THE HOUSING, A FIRST PISTON RECIPROCAL WITHIN THE BORE, A SLEEVE MEMBER PROJECTING FROM AN INNER FACE OF THE BASE MEMBER AND SPACED RADIALLY INWARDLY FROM THE OUTER CYLINDER AND HAVING AN APERTURE EXTENDING RADIALLY THERETHROUGH, A SECOND PISTON RECIPROCAL WITHIN THE SLEEVE MEMBER, SAID FIRST AND SECOND PISTONS DEFINING A FIRST EXPANSIBLE CHAMBER THEREBETWEEN, SAID SECOND PISTON DEFINING A SECOND EXPANSIBLE CHAMBER WITHIN THE SLEEVE MEMBER, SAID SECOND PISTON BEING SLIDABLE BETWEEN A FIRST POSITION WHEREIN THE SECOND PISTON BLOCKS FLUID FLOW BETWEEN THE FIRST AND SECOND CHAMBERS THROUGH THE APERTURE TO TRAP FLUID WITHIN THE FIRST EXPANSIBLE CHAMBER AND A SECOND POSITION WHEREIN THE PISTON PERMITS COMMUNICATION BETWEEN THE FIRST CHAMBER AND THE SECOND CHAMBER THROUGH SAID APERTURE TO ADJUST THE FIRST PISTON, BIASING MEANS INCLUDING A RETURN SPRING ACTING FOR BIASING THE FIRST PISTON INWARDLY OF THE BORE AND EXERTING A FORCE THROUGH HYDRAULIC FLUID IN THE FIRST CHAMBER TO MOVE THE SECOND PISTON FROM THE SECOND TO THE FIRST POSITION, AND A STATIC SEAL EFFECTIVE BETWEEN THE SECOND CHAMBER AND THE SECOND PISTON IN ITS FIRST POSITION TO PREVENT LEAKAGE OF TRAPPED FLUID FROM THE SECOND CHAMBER IN THE ADJUSTED POSITION OF THE SECOND PISTON WHEREBY A FORCE APPLIED TO THE SECOND PISTON BY PRESSURIZED FLUID SUPPLIED TO THE SECOND EXPANSIBLE CHAMBER IS TRANSMITTED TO THE FIRST PISTON THROUGH THE TRAPPED FLUID IN THE FIRST EXPANSIBLE CHAMBER AND IS EFFECTIVE TO MOVE THE SECOND PISTON A PREDETERMINED DISTANCE BETWEEN SAID FIRST AND SECOND POSITIONS PRIOR TO ANY FLUID BEING SUPPLIED TO THE FIRST EXPANSIBLE CHAMBER THROUGH SAID APERTURE. 